Re: [SI-LIST] : Buried Capacitors

Ray Anderson (raymonda@hsmpka-121)
Wed, 30 Jul 1997 10:04:25 -0700

This note from Ravinder somehow ended up in the admin mailbox. I'm
forwarding it to the list.

-Rayy

From: Ravinder Ajmani <ajmani@us.ibm.com>
To: <owner-si-list@silab.eng.sun.com>
Subject: Re: [SI-LIST] : Buried Capacitors
Date: Wed, 30 Jul 1997 11:40:55 -0400
Mime-Version: 1.0

Bob,
I have been doing some experiments with the buried capacitance. The board used
in our designs is approximately 6"X4", and there is a 3 mil separation between
Power and Ground planes. In my limited experiments, I have observed that on
average, radiated emissions from the board are reduced by about 5 dB in the
frequency range of 200 MHz to 1000 MHz for a board with the buried
capacitance. I have not studied the increase of emissions at some frequencies
due to board resonance. In both cases, the existing bypass capacitors were
left untouched. Reducing this Power/Ground separation to 2 mils didn't show
any significant improvement in performance
At the 1966 IEEE International Symposium on EMC (Santa Clara), there was a
paper on the effect of buried capacitance by S. Caniggia, V. Costa, and L.
Vitucci, of Italy, which you may like to refer.
Regards, Ravinder